1. Field of Invention
The present invention relates to an electromagnet and, more particularly, to a proportional electromagnet.
2. Related Prior Art
An electromagnet is used for turning electricity into magnetism and often used where intermittent movement is desired. The electromagnet includes a coil around a metal core which includes a bore defined in an end. The bore jeopardizes the density of the magnetism. Therefore, the magnetism is not constant in an operative stroke.
Referring to FIG. 4, shown is a conventional electromagnetic apparatus 5 that includes a magnetic circuit. The magnetic circuit goes from a coil unit 51 into a magnetic shield via a first bushing 52, a magnetic lining 53, a first air gap 54, a metal core 55. Then, the magnetic circuit is divided into two branches. One of the branches goes into a second air gap 56. The other branch goes into a supporting element 58 via a flange 57. Then, the magnetic circuit returns into the coil unit 51 via a second bushing 59. The bushings 52 and 59 and the air gaps 54 and 56 and the flange 57 are magnetic air gaps that exhibit a magnetic resistance about 400 to 800 times as high as magnetic metal about a same distance and area. Hence, an electromagnetic apparatus will operate inefficiently if includes many magnetic air gaps.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.